Substituted benzo [i] phenanthridines that have incorporated within their structure an 8, 9- methylenedioxy group can exhibit topoisomerase I-targeting activity. Structure–activity studies were performed to examine the influence of saturation at the 11, 12-positions of several substituted 8, 9-methylenedioxybenzo [i] phenanthridines. The activities of these dihydro analogues were compared to those of their unsaturated analogues. In addition, ...